1. Field of Invention
The present invention relates to switching power circuits, and more particularly to switching drive circuit for power converters or inverters.
2. Description of Related Art
A switching power circuit normally includes switching devices to drive inductive devices and/or a transformer. The switching devices connected to the transformer control energy transfer from the primary winding to the secondary winding of the transformer. The switching power circuit operates at high frequencies and allows a size and weight reduction. However, the switching losses, component stresses, and electric magnetic interference (EMI) are inherent problems. In order to reduce the switching losses, the popular phase-shift schemes of soft switching have been proposed for high frequency power conversion. Among them, the full-bridge (FB) quasi-resonant zero voltage switching (ZVS) technique are described in following prior arts:“Constant frequency resonant power converter with zero voltage switching” by Christopher, P. Henze, Ned Mohan, and John G. Hayes, U.S. Pat. No. 4,855,888; “Soft-switching PWM converters” by Guichao C. Hua and Fred C. Lee, U.S. Pat. No. 5,442,540; The active clamp techniques are disclosed for forward ZVS power converters such as: “Double forward converter with soft-PWM switching” by F. Don Tan, U.S. Pat. No. 5,973,939; for the half-bridge (HB) topology, an asymmetrical schemes is developed for ZVS, “Asymmetrical power converter and method of operation thereof” by Rui Liu, U.S. Pat. No. 6,069,798. In various ZVS converters, the parasitic leakage inductance of the transformer or additional magnetic components are employed as a resonant inductance or switches to generate the circulating current for achieving the zero voltage transition and switching.
FIG. 1 shows a full-bridge phase-shift switching power circuit. Switches 10, 20, 30 and 40 develop a full-bridge circuit. Switches 10 and 30 are connected to an input voltage VIN. Switches 20 and 40 are coupled to the ground. Controlling the on time of switches 10, 20 or controlling the on time of switches 30, 40 will regulate the power delivered to a load 50. An inductor 55 coupled in series with the load 50 will produce a circulating current to achieve soft switching. A high-side drive signal VA controls the on/off of the switch 10. A high-side switching signal SA generates the high-side drive signal VA through a high-side driver 12. A capacitor 15 and a diode 17 form a charge pump circuit to provide the power source to the high-side driver 12. The diode 17 is coupled to a terminal VCC to receive a regulated power source. The capacitor 15 is coupled to the diode 17 and the high-side driver 12.
Another high-side drive signal VC controls the switch 30. A high-side switching signal SC generates the high-side drive signal VC through a high-side driver 32. A capacitor 35 and a diode 37 develop another charge pump circuit to supply the power source to the high-side driver 32. The diode 37 is coupled to the terminal VCC to receive the regulated power source. The capacitor 35 is coupled to the diode 37 and the high-side driver 32. A low-side drive signal VB controls the switch 20. A low-side switching signal SB generates the low-side drive signal VB via a low-side driver 22. A low-side drive signal VD controls the switch 40. A low-side switching signal SD generates the low-side drive signal VD through another low-side driver 42. The low-side drivers 22 and 42 are coupled to the terminal VCC and the ground.
The object of the present invention is to provide a simple and economic solution to accomplish the soft switching. A switching drive integrated circuit is developed to generate drive signals VA, VB, VC, VD in response to an input signal, such as a PWM (Pulse Width Modulation) signal. A general and low-cost PWM controller such as 3842 can be used to generate the PWM signal.